Magnetic filtration system

ABSTRACT

A magnetic filtration system includes one or a plurality of collection units ( 1 ) comprising a magnet ( 4 ) disposed between a pair of plates ( 2, 3 ), one plate being magnetized North, the other, South. The plates are provided with facing apertures and facing pole pieces so that particles entering the recesses are both repelled from the apertures and attracted towards and retained in collecting regions between exposed facing plate portions.

DESCRIPTION

The present invention relates to a magnetic filtration system forfiltering ferrous and some non-ferrous material from a fluid in whichsaid material is in suspension.

The magnetic filter device of a previous application (9515352.4)(WO97/04873) (MARLOWE) comprises an annular magnet disposed between apair of annular metal plates. Fluid flows into the device throughrecesses in the metal plates, and returns through the centre of thedevice when used in conjunction with a conventional filter.

Another device (FREI) (U.S. Pat. No. 2,149,764) uses a series ofcylindrical magnets separated by a series of metal baffle plates, whichare magnetised through contact with the magnets. The flux fieldsgenerated are designed to collect particles on the plates themselves andalso around the edges of the perforations in the plates. A metal screenabuts the edges of the plates and is therefore magnetised throughcontact with it. The screen forms an envelope around the arrangement andis designed to increase the magnetised area in the actual flow path.Disadvantageously, however, the metal particles, which build up on thescreen, form an ever-increasing obstruction to flow. In addition, anyparticles collected on the plates are exposed to the flow, and are indanger of being washed off. In the present invention, the magnetic fluxdirection and properties are used to advantage as described laterherein.

A magnetic filtration system for filtering ferrous and some non-ferrousmaterial from fluid, in which said material is in suspension, comprisesinlet and outlet means. The system can advantageously be inserted atalmost any point in a fluid system. The filtration system comprises oneor a plurality of collection units that can be disposed in a housing.Magnetisable material, in particular ferrous particles and somenon-ferrous particles drawn along with the ferrous particles can becollected in the collection units. Particles are advantageouslymagnetically held out of the flow path, and therefore do not result inobstruction of flow. The collection units can be readily removed fromthe housing, to be dismantled, cleaned of any material collected andre-installed for re-use in the system. In an embodiment where the magnetis an electromagnet, when the electromagnet is active, material can becollected from the fluid, and when the electromagnet is deactivated, thematerial collected can be removed from the units and disposed from thesystem.

The present invention is applicable to fluid systems that are subject tohigh flow rate and pressure.

In accordance with one aspect of the present invention, there isprovided a magnetic filtration system for filtering magnetisablematerial from a fluid in which said material is in suspension comprisinginlet means and outlet means, in which one or a plurality of collectionunits is disposed, each collection unit comprising one or a plurality ofplates or plate arrays disposed either side of one or a plurality ofmagnets so that the plates or plate arrays have opposing polarities,wherein portions of the plates or plate arrays extend beyond part or allof an edge or edges of one or a plurality of said magnets, facing plateshave one or a plurality of apertures, and wherein facing aperturesdefine a region of magnetic repulsion, and facing plate portions definetherebetween, a region of magnetic attraction and magnetisable materialcollection, such that the magnetic flux fields thus created facilitatepreferential collection of magnetisable materials in the collectionregion between facing portions rather than in the region between saidfacing apertures.

It is an advantage that the facing collecting regions alternate withfacing apertures such that the attractive flux fields generated in thecollection regions and the repulsive fields disposed either side thereoffacilitate collection in a volume sandwiched between exposed facingplate portions. Particles can thus be retained in three-dimensionalspace rather than on merely the magnetised surface area that is exposedto fluid flow. Each collection unit thus offers greater capacity fordebris than that possible with the exposed surface area of its componentparts when disassembled. The repulsive forces in the apertures of eachcollection unit divert magnetisable material from the apertures so thatthey collect preferentially between facing plate portions rather than inthe apertures, to thus allow fluid to continue to flow through the uniteven at capacity.

Advantageously, the respective plates of adjacent collection unitshaving like polarity are disposed adjacent to one another so as tosubstantially restrict the collection of magnetisable particles to thecollection regions substantially within the interior of the collectionunits. An individual collection unit will have its own distribution ofmagnetic flux, part of which are regions of magnetic attraction betweenthe facing plate portions of the unit. If another unit is disposed sothat the respective neighbouring plates have unlike polarity, one North,the other, South, the flux existent within the collection unit (as anindividual) will be dispersed through the generation of further magneticfields of attraction between adjacent collection units. If thecollection unit is disposed beside another so that like poles ofadjacent plates are facing, then the repulsive forces thus createdbetween adjacent collection units will condense the attractive magneticflux towards the region between facing plate portions, more so than whenthere are no further adjacent units.

Advantageously, there is provided a housing made of a non-magnetisablematerial. This limits magnetisable material collection to the collectingregions within the collection units if the collection units are disposedin close proximity to the interior of said housing. The housing can bemade of a magnetisable material if said collection units stillfacilitate fluid passage therethrough even when filled with contaminant.

It is an advantage that there is provided a housing integral to a fluidflow system, said filtration system still permitting fluid flow thethrough even at capacity.

In one embodiment, each collection unit can be further separated from anadjacent collection unit by a spacing member. This allows for the betterutilisation of the available magnetic flux density.

It is an advantage that the spacing member is non-magnetic. It is alsoan advantage in certain instances that the spacing member is magnetic.The magnetisation or non-magnetisation of the spacing member isdiscussed later.

It is an advantage that the apertures in respective collection units,which are in closer proximity to the inlet means, are larger than thoseof units disposed nearer the outlet means. This provides collectionunits of varying magnetic strength along the direction of flow andalleviates any collection bias on the collection units closest to theinlet.

It is preferred that alignment means is provided for disposing theapertures and plate portions in facing plates of a collection unit insubstantial axial alignment. As fluid flows more smoothly throughapertures that are aligned, regions of particle collection surroundingthe apertures are thus exposed to a minimum of fluid turbulence, thusaiding in the retention of material collected. The presence of anaperture on a plate creates adjacent plate regions of like polarity,which thus generate between them, an axial region of magnetic repulsion.By aligning a pair of apertures of facing plates, the region of magneticrepulsion extends through an axial length of the collection unit. As theapertures are also the means for fluid flow through the collection unit,the path of fluid flow is also the region from which magnetisableparticles, suspended in the fluid, will be repelled. As the repulsiveforce acts radially, particles will tend to be redirected from the fluidflow path and repelled towards the adjacent region between the plateportions either side of the axial region of repulsion. The plateportions have between them, an attractive magnetic force actingsubstantially orthogonally to that of the repulsive flux field.Particles entering the axial recess between facing apertures are thusboth repelled from the axial recess and attracted towards the attractiveflux field of the gap or collecting region. Furthermore, as eachcollecting region has apertures either side of it, the attractive fluxlines in the collecting region are further condensed by the repulsiveflux lines extending orthogonally on either side. Condensing the fluxlines increases the magnetic field strength in that region. It is thecombined actions of these two fields that enables the apertures to bekept free of magnetisable particles and that enables particles to beheld in the collecting region despite high fluid flow (for example 400liters/minute) and fluid pressure (for example 7000 psi).

It is an advantage that further alignment means is provided fordisposing the apertures of respective collection units in substantialaxial alignment. This too will minimise the fluid turbulence betweencollection units, to any particles held magnetically in respectivecollection units.

Advantageously, said alignment means and further alignment meanscomprise a tab of given dimension on an internal edge of the plate andan axial unit having a groove of corresponding dimension to that of thetab, into which groove said tab can locate to provide a chosen axial andradial alignment of the facing plate portions and apertures of acollection unit and/or those of an assembly of collection units.

Preferably, the magnetic filtration system is further provided with flowdirecting means for directing fluid flow from the inlet means towardsthe apertures in said plates. The internal surface of the housing of thefiltration system can be contoured into a conical shape and the upperportion of the axial unit provided with a conical portion so that fluidfrom said inlet means is radially dispersed towards the apertures in themore or most proximal collection unit. Alternatively, a unit separatefrom the housing and the axial unit may be included between the inletmeans and the first collection unit, with an annular conical channel fordirecting fluid flow in the same manner.

Preferably, further slot-like apertures are provided in facing aperturesand facing plate portions to further enhance the magnetic flux densitybetween the facing plates of each collection unit. The provision ofslot-like apertures, which are aligned in facing plate portions, createsregions of magnetic repulsion, which are closer together than those ofthe first-mentioned apertures. The closer like poles are disposed to oneanother, the more intense the forces of magnetic repulsion between themwill be. The inclusion of such regions, for instance, in the middle of acollecting region further focuses the attractive flux fields in theseregions. The repulsive magnetic forces acting radially further condensethe flux density of the attractive flux lines, between facing plateportions, acting axially.

Advantageously, facing pole piece pairs are curved towards one anotherto further enhance the magnetic flux fields therebetween. As one polepiece is magnetised North and the other, South, the closer they aredisposed to one another, the stronger the flux between them will be, upuntil a point where the plates are saturated with magnetic flux from themagnet. In addition, as flux is dispersed through the edges of theplates, curving the edges of facing pole pieces towards each otherredirects the flux to an axial region between the plates. If the platesare left uncurved, the flux fields will extend radially from the edge ofthe plate. A field of attraction will still be generated between facingpole pieces, but of lesser strength than where they are curved towardsone another, where the flux fields emerging from facing pole pieces aresubstantially directed towards one another.

Advantageously, facing plates/plate arrays are separated by a distancewhich best utilises the magnetic flux emergent from the edges of saidfacing plates to attract and retain magnetisable material in the fluidand which also provides the collection capacity required. The larger thecollection capacity of the unit, the less frequently it will needcleaning. Thus the separation of the plates can be varied to determinethe required capacity for material as well as the magnetic fluxintensity distributions in the collecting regions and in the apertures.The plates are brought together in close enough proximity to enableaxial collection, in the collecting region between the internal portionsof each plate pair, of magnetisable particles, as small as one micron insize, despite high fluid flow (for example 400 liters/minute) and highpressure (for example, up to 7000 psi).

Advantageously, that the attractive flux lines between facing plateportions are substantially orthogonal to the repulsive flux lines in theapertures, such that magnetisable material entering the apertures, issubject to the influence of both attractive and repulsive flux fields.

Advantageously, internal surfaces of the housing are disposed in closeproximity to the outer portions of the plate/plate array pairs in orderto substantially constrain fluid flow in the filtration system toregions in which magnetic flux fields generated by plate/plate arraypairs facilitate the attraction and retention of the size range and typeor types of non-magnetisable particle input to the filtration system,for example, ferrous particles smaller than one micron.

Alternatively, where the housing is substantially larger than thediameter of the plates, the clearance between the collection units andthe housing may encompass regions beyond the efficient magnetic range ofthe collecting region. In such an instance, it is preferable to includeone or a plurality of distribution plates having further apertures insubstantial axial alignment with said plate apertures, which can bedisposed either side of one or more of the collection units to ensurethat all fluid is exposed to regions having magnetic flux density,similar to, or greater than a threshold required for particleattraction. The different sizes of particle and the type of particle insuspension in the fluid will have different such thresholds. Thesethreshold intensities also depend on the size and type of other materialin suspension as well as fluid flow and pressure. For instance, thethreshold intensity required to attract a particle which of a givensize, for example 1 micron, will rise if other forces acting on theparticle are increased, as when fluid pressure is increased or if fluidflow is increased.

Preferably, the housing comprises one or a plurality of sealablesections with interlockable threaded portions that enable said sectionsto be readily assembled or dismantled. The sections of the housing screwapart to facilitate insertion or removal of the collection unit assemblyinto or from the housing, and screw together to encase the assembly.When required, the assembly can be removed from the housing, cleaned ofany magnetisable material debris present and replaced inside for re-use.

Preferably, the housing is further provided with means for attachment toa fluid system.

Advantageously, isolation means may be provided for isolating (blankingoff) fluid flow to and from the filtration system to facilitate itsremoval from and insertion into the fluid system.

Advantageously, monitoring means for monitoring the presence and/oramount of material collected is disposed in the filtration system, sothat particle collection and therefore wear can be assessed withoutdismantling the system.

It is preferred that close down means is provided for enabling a system,of which said filtration system is a part, to be closed down if apre-determined level of debris collected is reached. If the wear of acomponent can be assessed at an early stage, other components sharingthe same fluid will be less likely to wear and complete system failure,perhaps involving substantially accelerated wear of several componentsand/or mechanical seizure, is thus less likely.

Advantageously, conventional filter media is disposed in the housing toremove non-magnetisable particles input to the system.

Advantageously, the magnet or magnets in the collection unit(s) is/areelectromagnet(s) having switch means for activating the electromagnet(s)to collect particles and for de-activating the electromagnet(s) tofacilitate release of any particles collected. This will facilitate moreconvenient removal of any material accrued in the collection unit beforeits re-use. The switch means, disposed outside the housing for manualaccess, is used to activate or de-activate the electromagnet dependingon whether the collection unit is in a filtration mode or in a cleaningmode. Alternatively, the switch means can be disposed inside the housingif external remote means of its operation are provided.

A further advantage of the present invention resides in the fact thatthe magnetic elements can impart some magnetism to the fluid flowingtherethrough and this can be used in a manner well known to thoseskilled in the art and therefore not described in more detail herein.

It is preferred that conventional cellulose fibre, metal or other filtermaterial is disposed in the magnetic filtration system to removenon-magnetisable material input to said system. Advantageously, thefilter material is placed downstream of one or a plurality of collectionunits.

In accordance with a further aspect of the present invention a method ofoperating a system for the removal of magnetisable particles from afluid system in which said particles are in suspension, includesproviding an apparatus comprising inlet means and outlet means, in whichone or a plurality of collection units is disposed, each collection unitcomprising one or a plurality of plates or plate arrays disposed eitherside of one or a plurality of magnets so that the plates or plate arrayshave opposing polarities, wherein portions of the plates or plate arraysextend beyond part or all of an edge or edges of one or a plurality ofsaid magnets, facing plates have one or a plurality of apertures, andwherein facing apertures define a region of magnetic repulsion, andfacing plate portions define therebetween, a region of magneticattraction and magnetisable material collection, passing fluid throughsaid apertures, retaining said particles in said regions of magneticattraction and repelling particles from said apertures.

Advantageously, said method of operating the system includes the stepsof detaching the plates from the magnets and then wiping off debris fromthe plates and the magnet, or alternatively, blowing the debris off theundismantled collection unit assembly with an air line. Particles areeasier to blow off if the air line is directed across the flux lines ofattraction rather than parallel to them.

In accordance with a still further aspect of the present invention, amethod of operating a system for the removal of magnetisable particlesfrom a fluid system in which said particles are in suspension, includesthe steps of providing an apparatus comprising inlet means and outletmeans, in which one or a plurality of collection units is disposed, eachcollection unit comprising one or a plurality of plates or plate arraysdisposed either side of one or a plurality of electromagnets so that theplates or plate arrays have opposing polarities, wherein portions of theplates or plate arrays extend beyond part or all of an edge or edges ofone or a plurality of said magnets, facing plates have one or aplurality of apertures in axial alignment, and wherein facing aperturesdefine a region of magnetic repulsion, and facing plate portions definetherebetween, a region of magnetic attraction and magnetisable materialcollection, passing fluid through said apertures, activating theelectromagnet to retain said particles in said regions of magneticattraction and repel particles from said apertures, de-activating theelectromagnet to release the particles from said regions of magneticattraction and disposing of said particles from said fluid system.

Advantageously, the method for activating and de-activating theelectromagnet includes passing current through coils of theelectromagnet.

Advantageously, monitoring the quantity and/or type of debris collectedincludes the steps of providing detection means for detecting thepresence of particles collected between facing plate portions, part ofwhich detection means extends in the collecting region of one or morecollection units, monitoring the type or quantity of material present,providing alarm means, setting off the alarm if material quantity risesbeyond a pre-determined rate or amount, providing closing down means forthe fluid system and closing down the fluid system if the quantity ofmaterial rises beyond a further pre-determined rate or amount.

Specific embodiments of the present invention will now be described withreference to the accompanying drawings in which:

FIGS. 1 to 9 show both internal plan view and cross-section of differentembodiments of collection unit, which can form part of a magneticfiltration system;

FIGS. 1a and 1 b are plan and side views of a collection unit accordingto the present invention and having radially extending bar magnets;

FIGS. 2a and 2 b are plan and side views of a collection unit accordingto another aspect of the present invention and having circumferentiallyarranged bar magnets;

FIG. 3 is a perspective view of part of a further embodiment of acollection unit;

FIGS. 4a and 4 b are internal and side views of a further embodiment ofa collection unit;

FIGS. 5a and 5 b are plan and side views of a collection unit accordingto a still further aspect of the present invention and having radiallyextending apertures and a cylindrical magnet;

FIGS. 6a and 6 b are plan and side views of a collection unit accordingto another aspect of the present invention and having circumferentiallyarranged slots and a cylindrical magnet;

FIGS. 7a, 7 b and 7 c are plan and side views of an alternativearrangement of collection unit and illustrates other orientations andshapes of apertures;

FIGS. 8a and 8 b are plan and side views of a still further arrangementof collection unit having an annular magnet inside which the aperturesare disposed

FIG. 9 is an internal plan view of a final collection unit having barmagnets and collection areas at the edges of the plates;

FIG. 10 is a cross-section through a magnetic filtration system;

FIG. 11 is an exploded view of a stack of collection units;

FIG. 12 is a cross-section of a plurality of collection units;

FIG. 13 is a cross-section through a magnetic filtration system withcontaminant indicator means;

FIG. 14 is a schematic diagram showing circuitry for a detector meansfor indicating the presence of magnetisable material collected in acollection unit;

FIG. 15 is a perspective view of an arrangement of collection units ofvarying dimension;

FIG. 16 illustrates a collection unit having an electromagnet;

FIG. 17 illustrates a magnetic filtration system having one or aplurality of collection units and a filtration medium for removal ofnon-magnetisable material, and

FIGS. 18a and 18 b are cross-sections of conventional filter mediaincluded in FIG. 17.

The arrows in FIGS. 10, 13 and 15 denote the direction of fluid flow.

FIGS. 1 to 9 show various embodiments of collection units. In FIGS. 1aand 1 b, a collection unit 30 has magnets 31 having faces of the samemagnetic polarity in contact with a collection plate 32. Respectivefaces of the magnets, of opposite polarity, are in contact with afurther collection plate 33. One plate is magnetised North, the otherSouth Apertures 34 in the plates are passage means for fluid flowthrough the unit. In FIG. 1. the magnets 31 are arranged radially. FIGS.2a and 2 b have plates magnetised in a similar manner, but with themagnets arranged circumferentially. The dotted lines in FIGS. 1b and 2 bshow alternative profiles of plates. The dotted lines in FIGS. 1a and 2a show slot-like apertures that may be added to the plates. Thesearrangements generate three-dimensional collection regions between theplate pairs other than where the apertures are aligned, thus offering arelatively large capacity for contaminant. The distance between theplates, the number and size of apertures and the overall magnetic fieldstrength can be varied to suit the required flow rate desired throughthe unit and the size and type of contaminant in the fluid. The smallerthe aperture and the closer the plates, the greater the magnetic fluxdistributions around the collecting region. This then facilitates theability of the unit to attract and retain very small magnetisableparticles.

The number and size of the apertures in each plate will determine theoverall cross-sectional area available to fluid flow. The size andnumber of apertures can thus be varied to correspond with the dimensionsof an inlet or outlet of the fluid system. If the total cross-sectionalarea of the apertures is made smaller than that of the fluid system,there will be an increase in fluid velocity where fluid flow is moreconstricted. If the total cross-sectional area of the apertures islarger than that of the fluid system, there will be a reduction in fluidspeed where fluid flow is dilated. If the fluid system can withstand thereduction in fluid speed across the filtration system, it may be anadvantage to slow the flow to delay particles for a longer period oftime, to thus enable them to be captured more easily. In addition, theaperture dimension should be larger than the largest particle likely tobe suspended in the fluid, to prevent occlusion of the apertures.

Apertures having the same width, if aligned, will define between them anaxial aperture of corresponding width. The narrower the axial aperturewidth, the greater the repulsive force inside it and therefore thegreater the ability of the repulsive magnetic flux to redirect particlesfrom the fluid flow path towards the collecting regions. However, areduction in aperture dimension produces a corresponding reduction inthe cross-sectional area available for flow unless there is acorresponding increase in the number of apertures. Aperture width isthus optimised for both required flow throughput and magnetic fluxstrength for the attraction and retention of particles, of a size rangeand type, present in the fluid system. When facing plate portions arealigned with one another, the greater the edge width, the wider thecollecting region and therefore the greater the capacity for collectionof material. However, the capacity for collection is moderated by thetotal axial recess volume required for fluid throughput. The repulsiveeffect from an axial recess is stronger at the edge of a region ofmagnetic attraction than it would be, for instance, in the middle of thecollecting region. Thus, for a required collection capacity, it may bemore advantageous to have narrower but more numerous plate portions sothat the repulsive forces in the axial recesses are utilised to besteffect.

Because of the chosen axis of polarisation of the magnet, magnetic fluxfrom the magnet face in contact with the plate is then preferentiallydispersed and concentrated towards the peripheral edges of the plates.The aperture dimension, the number of apertures and the thickness of theplate are all factors that determine the overall peripheral edge surfacearea available for magnetic flux dispersion. The peripheral surface areacan thus be varied to utilise the available magnetic flux from themagnet attached thereto. The magnetic flux emerging from a surface isgiven by the equation:

Φ_(M) =B _(M) ×A _(M)

where B_(M) is magnetic flux density of the magnet material, A_(M) isthe cross-sectional area (in cm²) of the magnet through which the fluxacts and Φ_(M) is the magnetic flux through area A_(M). The flux Φ_(M)will be dispersed through a peripheral surface area A_(P) of the edges.The flux Φ_(M) divided by A_(P) should not exceed the saturation fluxdensity for the material of which the plate is made. For mild steel,this figure is around 15,000 Gauss.

The strength of the magnet in any of the embodiments is advantageouslytailored to suit the optimum saturation characteristics of theperipheral surface area of the plates. Consideration should be given tothe increase in magnetic flux generated when like poles of adjacent coreunits interact with each other. The introduction of spacing units(discussed later herein) isolates the magnetic flux densities created ineach core unit and might be employed to alleviate the above problem.

For each design, there will be an optimum flux density for the availableperipheral area of the plate. Consequently, either the peripheral areamay be selected to match the flux density available from a given magnet,or the magnet strength may be selected to suit the available peripheralsurface area. Whilst over-fluxing will not detract from the performanceof the invention, it will be appreciated that best production costs canbe achieved by adopting this approach. Exceeding the optimum magneticflux possible for a given plate dimension means that flux lines extendthrough the outer radial face of the plate, thus enabling particles tobe collected on the plate outside of the collection unit. Collection ofparticles is preferably inside the unit where they can be held onto morestrongly.

Provision of a greater magnetic flux than required can enable the systemto have magnetic flux in reserve. The ability to attract and retainparticles can then be increased by increasing the peripheral edge areaby, for instance, adding another plate or replacing the plate with thatof a greater thickness. The addition of the aforementioned slot-likeapertures in the plates increases the peripheral surface area furtherand can utilise any excess flux to enhance the retentive function of thecollection unit.

By under-sizing the magnet strength, one fails to fully utilise theavailable peripheral area and hence, the retentive abilities of thecollection units are not optimised.

FIG. 3 shows a collection unit or part of a collection unit having pairsof collection plates 35, 36 of opposite magnetic polarity, throughcontact with magnets 37. Adjacent collection plates 35 thus have likepolarity. This arrangement permits the use of non-circular magnets.Magnetisable material can be collected between plate pairs 36 and 37 andretention of particles therebetween is enhanced by the relativeproximity and/or intensity of like fields from one or a plurality ofadjacent plate pairs.

A collection unit in FIGS. 4a and 4 b has plates having pole pairs 38,39 magnetised through contact with a magnet 40 disposed therebetween.Through contact with the same magnet face, adjacent plates 38 have likepolarity. Fluid flows in the apertures between adjacent plates as wellas in the recesses in the plates. Magnetisable material in suspension inthe fluid will be repelled from these apertures and recesses andattracted to collecting regions between the pole pairs. This arrangementallows the magnetisation of a plurality of isolated plates throughcontact with one magnet, and the creation of adjacent repulsion zonesalong the length of the magnet. The dotted lines on FIG. 4a show thatfurther apertures can be added to the plates 38, 39 to enhance theability of the collection unit to retain magnetisable particles.

Collection units in FIGS. 5a, 5 b, 6 a and 6 b have cylindrical magnets41, opposite faces of which magnetise plates 43, 44, North and Southrespectively. The unit illustrated in FIGS. 5a and 5 b has radiallyextending apertures 45 larger at the perimeter of the plate than nearerthe centre. Repulsive forces are greater where the aperture is narrower.A gradation in magnetic field strength is provided across the radialspan of each aperture, and therefore induces a radial gradation in thesize and/or type of particle collected between the plates.

The collection unit in FIGS. 6a and 6 b has circumferentially disposedand extending apertures 46. A gradation in magnetic field strength isprovided across the circumferential span of each aperture, and thereforeinduces a circumferential gradation in the size and/or type of particlecollected between the plates. Repulsive forces are stronger in regionssurrounded by more edges.

The collection units in FIGS. 7a, 7 b and 7 c illustrate other shapes ofapertures 47, 48 for collection plates. The uniform aperture of FIG. 7adefines a region of uniform magnetic flux density across thecross-section of the aperture. In FIG. 7b, the narrower slot-likeapertures in the plate define portions of the plate of like polaritydisposed in relatively close proximity, and around which, the magneticflux density is thus enhanced. The closer the spacing between likepoles, the greater the repulsive effect between them, and therefore,material is less likely to accumulate in the passage means for fluid.

A collection unit in FIG. 8 has collecting regions 49 arranged insidethe aperture of an annular magnet 50. Plates 51, 52 abut opposite facesof the magnet 50. Such an arrangement could facilitate the wiring of anelectromagnet. For example, an electromagnet coil and its connectionsmay be easier to isolate from fluid flow in this arrangement. In afurther variation of this arrangement (not shown), a circular plate pairis centrally disposed either side of the magnet, having a large enoughouter diameter to abut it, but a small enough inner diameter to exposepart of the magnet. The exposed magnet faces could then additionallyhave disposed thereon, further plate portions, adjacent to the centralplate pair or disposed substantially concentric to that of the centralplate.

FIG. 9 shows a collection unit having a plurality of radially arrangedmagnets 53 with like poles in abutment with a collection plate 54,opposite poles in abutment with a facing collection plate (not shown).This arrangement facilitates the adjustment of the magnetic flux densityof the collection unit through variation of the number of magnetspresent in the collection unit.

The plates/plate arrays shown in FIGS. 1 to 7 can be further providedwith narrow longitudinal apertures extending radially orcircumferentially. Examples of these are represented by dotted lines onFIGS. 1a, 2 a and 4 a. This will produce zones of enhanced magneticrepulsion. The perimeter portions of facing plate portions in any of theembodiments can also be curved towards one another to enhance thestrength of the attractive magnetic flux between them. Examples of theseare represented by dotted lines on FIGS. 1b, 2 b, 4 b, 5 b, 6 b, 7 c, 8b, and shown in solid lines on FIGS. 10 to 13 and 15 to 17. One of themajor advantages of the present invention resides in the provision ofthe recesses or apertures which allow the magnetic flux density to beconcentrated in the collection region whilst also creating a region ofmagnetic repulsion within the recesses which prevents the build-up ofmagnetic particles therein, thereby avoiding blocking therein andobstruction of flow. This feature enables flow to be maintained withinthe filter even when the filter has reached contaminant capacity, thiscapacity being approximately the volume defined between exposed facingplate portions. As mentioned earlier, the capacity of the unit shouldoptimally suit the degree of contamination of the fluid system, the sizeand type of particle that makes up this contamination and the systemflow rate and pressure.

Referring to FIGS. 10 to 13, a collection unit 1 is formed from a platearray pair 2, 3 between which, one or a plurality of magnets 4 isdisposed. The plates attach to the magnet by magnetic attraction. Eachplate array comprises pole pieces 5 and recesses or apertures 6, whichare further provided with slots 7. Facing pole pieces are curved towardsone another to enhance the magnetic flux between them. One plate arrayis polarised North, the other South through contact with the magnet 4.The unit 1 is mountable onto a non-magnetisable rod 8. The diameter ofthe rod 8 is smaller than the internal diameter of central holes in theplates and the magnets. In this specific embodiment, a collection unitis assembled by placing a magnet between a pair of plates. In specificembodiments, for plates of diameter ranging between 30 to 50 mm and ofthickness ranging from 1 to 3 mm, the plate separation can range from 5to 10 mm. Other plate separations, thicknesses, and diameters can beused. Apertures and pole pieces are symmetrically arranged about theplate. If, for example, there are eight apertures, approximately 7 mm inwidth and length, the eight pole piece pairs respectively, in between,will occupy the remaining perimeter. For a given size of plate, thesizes of aperture and pole piece required will determine the number ofapertures and pole pieces that can be accommodated in a givencircumference. For the examples given, the slots in the plates can varybetween 1 and 2 mm in width.

As shown earlier, the magnetic flux density of the magnet can then bechosen for a specific plate dimension. In a specific embodiment, curvingthe outer portions of facing pole pieces towards each other, so thatthat facing edges are separated by a distance that is approximately halfthat of the uncurved plate separation, the flux intensity between theplates can approximately double. Thus, the larger the plate separationthe greater the capacity of the collection unit, but facing pole piecestowards one another, maintains nearly the same capacity (as that of theuncurved pole pieces) but with the advantage of the properties ofenhanced magnetic flux fields obtainable with closer plate separation.The rod is provided with an axial recess or groove 10 on an outer face.The plates 2, 3 are further provided with a tab 11 on an internalsurface which locates into said groove 10, to ensure that the recesses 6and pole pieces 5, respectively, of adjacent collecting units, are inradial and axial alignment if the collection units are identical, or inan alternative radial alignment if the collection units are notidentical. The groove provided on the rod will thus only accept thecollection units in their respective chosen orientation of recesses andpole pieces. A spacer 9 is optionally mountable onto the rod so that itseparates a further unit, which could be identical to, or have differentdimensions to that of the first-mentioned unit, to be mounted on afterit. The spacer may be used to modify the magnetic flux pattern as andwhen desired. For example, the spacer enables separation of the magneticfluxes in adjacent collection units, which might otherwise beover-saturated due to the combining effect of like poles beingpositioned directly adjacent each other. It has been found that whenlike poles are placed adjacent to each other, the combined magnetic fluxcould, in some circumstances, be greater than the optimum for theavailable peripheral surface area. The use of a non-magnetisable spacerfacilitates prevention of dispersal of magnetic flux from adjacent coreunits. Magnetisable spacers, on the other hand, can cause dispersion ofthe magnetic flux, which can be used to advantage should one wish totailor the degree of saturation in the vicinity of the collectionregion. Adjacent units are oriented so that like poles on adjacentcollecting units are facing. Further collection units are mounted on therod and separated in a similar manner.

A distribution plate 12 (shown in FIGS. 10 and 13) preferably made of anon-magnetisable material abuts the first plate in the line of flow. Acirclip or other retaining means 13 is disposed on one side of thedistribution plate and in abutment with the last mounted collection unitto maintain the collection units in their axial locations. The rod 5 isfurther provided with flow distribution means 14 that can be domed inshape as shown in FIGS. 10 and 13 or conical in shape as shown in FIG.17. An internal surface 24 of the housing is conical in shape and flowdistribution means 14 is an integral part of the rod 8. Fluid enteringthrough the inlet is thus directed towards the apertures in the mostproximal plate.

The rod 8 mounted with collection units 1 is disposed in a housing 15divided into two parts, which interlock by means of threaded surfaces 16and which can be sealed by sealing means 17 in the form of, for example,a rubber ‘O’-ring. The two parts of the housing may be screwed apart toaccess the assembly of collection units, as may be the case when theunit is inspected for evidence of mechanical wear and/or if it requirescleaning. They can then be screwed together to re-enclose them, when thefiltration system is ready for re-use.

Alternatively, the collection unit assembly illustrated in FIGS. 10 and12 may be disposed in housing means that is integral to the fluid flowsystem. As there is no obstructive barrier across the entirecross-section of flow, the magnetic filtration assembly has no minimumfluid pressure or flow requirements. Therefore, these factors do notplace constraints on the location of the collection units. The housingmay be a part of a fluid line, part of the fluid system housing or otherpart of the fluid system. The housing may be made of a material toenable the filtration system to withstand the fluid pressure of thesystem of which it will be part. For example, a unit having fourcollection units housed in a housing, approximately 135 mm long and 90mm in diameter, made of aluminium can withstand pressures of up to 7000psi.

Detector means 18, 19 (FIG. 13) can be provided for detecting thepresence of magnetisable material collected between said pairs of polepieces. Said means could be mounted in the housing 15 and connecteddirectly, or accessible remotely, to indicator means on the outside ofthe housing or to a remotely located indicator unit.

One form of detector means 18, 19 comprises an insulator 20 disposed inan aperture in the housing 15. A probe 21 made of conducting material,is disposed inside the insulator 20 so that one end of the probeprotrudes into the collecting region between one of the pairs of polepieces, and the other end of the probe remains outside the housing.Retaining means 22 retains a conducting connector 23 on the part of theprobe 21 outside the housing. It also retains a sealing means 24 againstthe aperture in the housing and the insulator 20. In this embodiment,the build up of metal particles between the probe and the plate willcomplete the circuit.

Referring to FIG. 14, in another embodiment, a probe 73 is connected toa signal processor 65, which is also connected to a pole piece 5 of oneor more collection units via an insulator 66. A switch 67 activates apower supply 68, which provides current to the probe 73 via a furtherswitch 72 and a timer 69. The switch 72 can be automatically activatedby the timer 69, which can be controlled by a computer 70. The signalprocessor 65 is additionally connected to display means 71, the switches67, 72 and the timer 69. The presence of magnetisable material on theplate will vary the electrical characteristics of the circuit. Theelectrical characteristics will depend on the type and size of materialin the fluid system. In an alternative circuit, the presence of debriscollected between the probe and the pole piece 5 has to be greater thana pre-determined value to enable the circuit to be completed. Theadvantage of the other embodiment over the latter means that debris canbe detected in very small amounts. The debris does not have to build upto such an extent that it will complete a circuit. The electricalproperties (voltage/current/resistance) of this connection can then bedisplayed on the display 71 as well as relayed to the computer 70. Thesystem can be calibrated to known contaminant levels to enable referencedata to be provided when the system is in use. Data from the signalprocessor can be output to display means and/or a monitoring computer.Detection may be a continuous process or one which is performed at givenintervals. The frequency of the detection process can be increased whendebris build up accelerates beyond a pre-determined rate. An alarm 74,which may be audio or visual, can also be activated when debris build-uprises to a pre-determined level or if it rises at a rate greater than afurther pre-determined rate. Following receipt of data from the signalprocessor, the computer 70 may have facility, via the switch 67, forshut-off of the fluid system operation if a pre-determined thresholdlevel of system contamination is reached.

In an arrangement having substantially common collection units, fluidcontaining metal contaminant will flow into the recesses and metaldebris builds up between pairs of pole pieces 5. Detector means 18disposed by the first collection unit encountered by the flow will thenact as an indicator of early build up of debris in the filtrationsystem. Because some of the metal particles suspended in the fluid areremoved as fluid first flows through a collection unit, the fluid whichflows into the next collection unit therefore contains less metalcontaminant. Thus, the collection unit furthest from the inlet will takethe longest to fill with debris. Detector means 19 disposed by thiscollection unit will indicate when the fluid filtration system issubstantially filled with contaminant.

The detector means could also be used to indicate the quantity of debrispresent, and not just its presence. In one example, once the circuit isconnected, different amounts of debris will offer respectively differentresistances to the passage of current in the circuit. Once calibrated,current or other readings could then relate to the amount of debriscollected.

Greater numbers of collection units can be stacked together (FIG. 12) tofurther enhance the collection capacity of metallic debris, by thefiltration system.

In a further embodiment, distribution plates are disposed at the platesnearest the inlet and outlet means, and between adjacent collectionunits.

In another embodiment, the distribution plate may be omitted dependingon the flow rate required through the device and the clearance betweenthe outer diameter of the metal plates and the housing.

In a further embodiment shown in FIG. 15, the collection units can beprovided with successively larger recesses or apertures to vary themagnetic flux density along the direction of flow. Collection units withsmaller recesses or apertures will have greater magnetic flux intensityin both collecting portions and in fluid pathways. The axialdistribution of flux intensity will thus produce a gradation in the sizeand or type of particle that is input to the system and also thereforeprevent occlusion of the first-impinged collection unit beforesubsequent collection units are filled. In FIG. 15, collection unit 75is disposed closer to inlet means (not shown) to the collection unitassembly than collection unit 77. Unit 75 has larger apertures thancollection unit 76, the apertures of which, are larger than those ofcollection unit 77. Collection unit 77 therefore exerts a greatermagnetic flux density than collection unit 75. For example, particlesthat are more easily magnetised may be captured with comparativelywidely spaced plates and/or comparatively larger recesses. Less easilymagnetised particles may be captured between more closely packed platesand/or with comparatively smaller recesses. For example, iron-basedparticles may be captured more easily than say aluminium and phosphorbronze. Indeed, it is quite possible to capture particles having a verylow magnetic permeability, so long as the spacing and recesses aredefined accordingly.

Collection units can be removed from the fluid system for inspection ofmaterial collected therein, for example, for component conditionmonitoring, and/or cleaning of any material collected. At its places ofinsertion into a fluid system, the filtration system can be disconnectedat both or either its outlet and/or inlet using isolation means (notshown) to maintain fluid in the fluid system (if so desired) whilst thefiltration system is disconnected from it. To remove material from theunits shown in FIGS. 10 and 13, the housing 15 is screwed apart and thecollection unit assembly is removed. The circlip is removed to allow thecollection units to be removed from the rod 8. The plates, held on bymagnetic attraction to the magnet, are pulled off the plates. Onceremoved from the plates, material attached to the plates is no longermagnetised and these can be wiped off. Material attached to the magnetcan also be wiped off.

Alternatively, the collection unit assembly need not be dismantled wherean air line is used to blow off any debris collected. The cleaned coreunit can then be fitted into the two parts of the housing, sealed insideand re-fitted to the fluid system.

In an embodiment where the housing is integral to that of the fluidsystem, the collection unit assembly is removed and re-inserted by meansavailable to that particular housing.

In FIG. 16, an electromagnet 80 is in the form of a coil of wire 81wrapped around a core 82 made of soft iron or other magnetisablematerial. As is known to those skilled in the art, when current ispassed through the coil, a magnetic field is induced in its vicinity,one end of the coil magnetised North, the other, South. Depending on thedegree of magnetisation required, the plates 2, 3 can be disposedagainst or in close proximity to the electromagnet to gain the magneticpolarity of the respective side of the coil. Alternatively, themagnitude of the current to the coil, the type of material in the coiland the number of turns in the coil can be varied to the produce thedesired magnetisation required for respective plate designs.

To operate a filtration system incorporating an electromagnet, currentis passed to the coil to place the system in a filtration mode ofoperation. This current can then be switched off when the system is incleaning mode. At the points of its insertion in a fluid system, thefiltration system could then be disconnected at both or either itsoutlet and/or inlet using isolation means (not shown) as describedearlier. When the current is switched off and the electromagnetde-activated, the no flux extends through the plates or to the particlescollected there. As these particles are no longer held on the plates andelectromagnet(s) by magnetism, they are much easier to remove than whenthe electromagnet is activated. The particles can be removed by flushinga fluid through the assembly. These can be collected for more detailedanalysis of component condition.

The filtration system may be provided with a housing that facilitatesthe loading of a further clean collection unit assembly as soon as acontaminated one is removed. This advantageously reduces fluid systemdown-time when the filtration system is removed. The assemblyreplacement could be automated if the unit is mounted on a motorised orhydraulically operated housing. If detection means, for determining thequantity of material collected, is used in conjunction with such anassembly, replacement of the collection unit assembly could be triggeredat regular intervals or if a pre-determined level of material isattained. As mentioned before, where close down or shut-off means isprovided in the fluid system, this can be activated if contaminationlevels rise beyond pre-determined acceptable values.

In a still further embodiment shown in FIG. 17, conventional filtermedium 90 made of cellulose fibre, metal or other material could beincluded in the magnetic filtration system to remove non-magnetisablematerial input to the system. When the filter medium is placeddownstream of one or more collection units, the capacity of the mediumis taken up by only non-magnetisable material, as the collection unitsremove the magnetisable particles from the fluid before it reaches thefilter medium. In the examples shown in FIGS. 18a and 18 b, the medium90 presents a smaller cross-sectional area to the flow than that of theoverall cross-section of its enclosing means 91 so that, even atcapacity, fluid is still able to flow past or through the conventionalfilter medium 90.

What is claimed is:
 1. A magnetic filtration system for filteringmagnetisable material from a fluid in which said magnetisable materialis in suspension comprising: inlet means; outlet means; a plurality ofcollection units disposed between the inlet means and the outlet means;each collection unit comprising a magnet and at least two plates orplate arrays disposed on other side of the magnet so that the plates orplate arrays have opposing polarities, wherein portions of the plates orplate arrays extend beyond part or all of an edge or edges of saidmagnet, facing plates of each of said collection units have one or aplurality of apertures and facing pole pieces between said aperturescreate magnetic flux fields which define one or more collection regionsof magnetic attraction and magnetisable material collection, tofacilitate collection of said magnetisable material in the collectionregions between exposed facing plate portions, wherein facing collectionregions in each said collection unit are disposed between facingaperture such that said magnetic flux fields generated in the collectionregions facilitate collection of said magnetisable material in a volumesandwiched between exposed facing plate portions, and wherein therespective plates of adjacent collection units having like polarity aredisposed adjacent to one another so as to substantially restrict thecollection of said magnetisable material to the collection regions.
 2. Amagnetic filtration system as in claim 1 further comprising a housingmade of non-magnetisable material.
 3. A magnetic filtration system asclaimed in claim 1, further comprising a housing having means forconnection to a flow system, the collection units being located in thehousing.
 4. A magnetic filtration system as claimed in claim 1, whereineach collection unit is further separated from an adjacent collectionunit by a spacing member.
 5. A magnetic filtration system as claimed inclaim 4, wherein said spacing member is non-magnetic.
 6. A magneticfiltration system as claimed in claim 4, wherein said spacing member ismagnetic.
 7. A magnetic filtration system as claimed in claim 1, whereinthe apertures in respective collection units, which are in closerproximity to the inlet means, are larger than those of units disposednearer the outlet means.
 8. A magnetic filtration system as claimed inclaim 1, further comprising alignment means for disposing the aperturesand pole pieces, in the facing plates of a collection unit, insubstantial axial alignment.
 9. A magnetic filtration system as claimedin claim 8, further comprising further alignment means for disposing theapertures of respective collection units in substantial axial alignment.10. A magnetic filtration system as claimed in claim 9, wherein saidalignment means and further alignment means comprise a tab of givendimension on an internal edge of the plate and an axial unit having agroove of corresponding dimension to that of the tab, into which groovesaid tab can locate to provide a chosen axial and radial alignment ofthe facing plate portions and apertures of one or more of saidcollection units.
 11. A magnetic filtration system as claimed in claim1, further comprising flow directing means for directing fluid flow fromthe inlet means towards the apertures in said plates.
 12. A magneticfiltration system claimed in claim 1, further comprising slot-likeapertures in said apertures and facing plate portions to further enhancethe magnetic flux density between the facing plates of the collectionunits.
 13. A magnetic filtration system as claimed in claim 1, whereinthe facing pole pieces are curved towards one another to further enhancethe magnetic flux fields therebetween.
 14. A magnetic filtration systemas claimed in claim 1, wherein the facing plates or plate arrays areseparated by a distance which best utilises the magnetic flux emergentfrom edges of said facing plates or plate arrays to attract and retainsaid magnetisable material in the fluid and which also facilitates arequired collection capacity.
 15. A magnetic filtration system asclaimed in claim 1, wherein the attractive flux lines between facingpole pieces are substantially orthogonal to repulsive flux lines in theapertures, such that the magnetisable material entering the apertures,is subject to the influence of both attractive and repulsive fluxfields.
 16. A magnetic filtration system as claimed in claim 1, furthercomprising a housing and wherein internal surfaces of the housing aredisposing in close proximity to the outer portions of said facing platesor plate arrays in order to substantially constrain fluid flow in thefiltration system to regions in which magnetic flux fields generated bysaid facing plates or plate arrays facilitate the attraction andretention of the size range and type or types of the magnetisablematerial input to the filtration system.
 17. A magnetic filtrationsystem as claimed in claim 1, further comprising one or a plurality ofdistribution plates having further apertures in substantial axialalignment with said plate apertures, with each of the one or pluralityof distribution plates being disposed on either side of one or more ofthe collection units to ensure that all fluid is exposed to regionshaving magnetic flux density similar to, or greater than, a thresholdrequired for particle attraction.
 18. A magnetic filtration system asclaimed in claim 2, wherein the housing comprises one or a plurality ofsealable sections with interlockable threaded portions that enable saidsections to readily assembled or dismantled.
 19. A magnetic filtrationsystem as claimed in claim 2 wherein the housing includes means forattachment to a fluid system.
 20. A magnetic filtration system asclaimed in claim 1, further comprising isolation means for isolatingfluid flow to and from the filtration system to facilitate removal offluid flow from and insertion into the filtration system.
 21. A magneticfiltration system as claimed in claim 1, further comprising monitoringmeans, for monitoring the presence and/or amount of said magnetisablematerial collected, in the filtration system.
 22. A magnetic filtrationsystem as claimed in claim 21, further comprising system close downmeans which is actuated upon detection of a pre-determined level ofmaterial collected in the filtration system.
 23. A magnetic filtrationsystem as claimed in claim 1 further comprising a filter medium disposedin the housing to remove non-magnetisable particles input to the system.24. A magnetic filtration system as claimed in claim 1, wherein at leastone of said collection units includes an electromagnet and switch meansfor activating the electromagnet to collect said magnetisable materialand for de-activating the electromagnet to facilitate release of saidmagnetisable material collected.
 25. A magnetic filtration system asclaimed in claim 1, further comprising cellulose fiber, metal or otherfilter material to remove non-magnetisable material input to saidsystem.
 26. A magnetic filtration system as claimed in claim 25, whereinsaid filter material is placed downstream of one or a plurality of saidcollection units.
 27. A method for removing magnetisable material from afluid in which said magnetisable material is in suspension, comprising:providing an apparatus as claimed in claim 1, passing the fluid throughsaid apertures, and attracting and retaining said magnetisable materialin said collection regions.
 28. A method as claimed in 27, furthercomprising detaching the plates from the magnet and mechanical removalof said magnetisable material from the plates and the magnet or magnets.29. A method as claimed in claim 27, further comprising removing saidmagnetisable material collected, in an undismantled collection unit,with an air line.
 30. A method for removing magnetisable material from afluid in which said magnetisable material is in suspension, comprising:providing an apparatus as claimed in claim 1 wherein at least one ofsaid collection units includes an electromagnet and switch means foractivating the electromagnet to collect said magnetisable material andfor de-activating the electromagnet to facilitate release of saidmagnetisable material collected, passing the fluid, via a fluid system,through said apertures and attracting and returning said magnetisablematerial in said collection regions, activating the electromagnet toretain said magnetisable material in said regions of magneticattraction, de-activating the electromagnet to release said magnetisablematerial from said regions of magnetic attraction, and disposing of saidmagnetisable material from said fluid system.
 31. A method as claimed inclaim 30, wherein the activating and de-activating the electromagnetincludes passing through coils of the electromagnet.
 32. A method formonitoring the quality and/or type of magnetisable material collectedcomprising: providing an apparatus as claimed in claim 1, providingdetection means for detecting the presence of magnetisable materialcollected between facing portions of the plates or plate arrays, part ofwhich detection means extends in the collection region of said one ormore collection units, monitoring the type or quantity of saidmagnetisable material present, providing alarm means, setting off thealarm if the quantity of said magnetisable material rises beyond apre-determined rate or amount, and providing closing down means for afluid system supplying fluid to said apparatus, and closing down saidfluid system if the quantity of said magnestisable material rises beyonda further pre-determined rate or amount.
 33. A magnetic filtrationsystem as claimed in claim 1, wherein said facing apertures in saidplates define a region of magnetic repulsion.
 34. A magnetic filtrationsystem as claimed in claim 33, wherein said facing plates comprises aplurality of said facing apertures defining a plurality of regions ofmagnetic repulsion.
 35. A method as claimed in claim 27, wherein saidfacing apertures in said plates define a region of magnetic repulsion.36. A method as claimed in claim 35, wherein said facing plates define aplurality of regions of magnetic repulsion from which magnetisablematerial is repelled.